1. Field of the Invention
This invention relates to an improved structure for a transformer. More particularly, it relates to an improved inverter transformer structure operable at high frequencies in a power supply.
2. State of the Prior Art
In the development of power supplies for use with electronic components, particularly those circuits utilizing integrated circuits, it has been found to be advantageous to utilize a transformer having a ferrite core with a primary winding for coupling to a source of alternating signals, and a secondary winding center-tapped and arranged to operate push-pull to drive a bridge rectifier. It is desirable that transformers for use in such circuitry function with low leakage inductance at rates of 200 kHz or higher. Further, it is desirable that such transformers be adaptable for providing output voltages in a predetermined range, dependent upon the wiring interconnection of the transformer. For example, it is desirable that a transformer structure be available for supplying drive for a rectifier circuit that will ultimately selectively provide through an associated voltage regulator an output of 2 volts, 5 volts, 12 volts or 24 volts.
It is desirable that a transformer structure for use in the type of power supply environment described above be inexpensive and easy to construct. In this regard it is desirable that the transformer structure be compatible with use on printed circuit assemblies, and that the transformer not be complex to manufacture.
Attempts have been made in the prior art to adapt various manufacturing techniques to make transformers that have varying functional characteristics. A system for die casting core windings is described in U.S. Pat. No. 3,477,051 to Clark et al, and a specialized pulse transformer and method of manufacturing is described in U.S. Pat. No. 3,483,495 to Clark et al. Examination of the teaching of these patents makes it abundantly clear that the fabrication process is complex. U.S. Pat. No. 4,311,979 to Graul describes a method and structure for generating a transformer having layered windings. It has been pointed out in the prior art that the so-called layer transforms have developed operational problems, often times apparently traceable to localized heat buildup.
U.S. Pat. No. 3,144,628 to Rabins describes a power transformer having cylindrical independent windings concentrically arranged, and capable of interconnection in selected series/parallel arrangements for adjusting the turns ratio. The arrangement is specified for providing a given output voltage for different input voltages.
U.S. Pat. No. 2,765,448 to Duffing, and U.S. Pat. No. 2,907,968 to Thurk each describe forming coils for switching reactors constructed from interconnected independent segments.
U.S. Pat. No. 4,249,229 to Hester describes a transformer utilizing flexible electrical cable for making auxiliary couplings to the transformer.
In addition to the interconnected independent segments for forming a coil mentioned above, U.S. Pat. No. 3,453,574 to DeParry describes a high frequency transformer wherein the primary and secondary windings are constructed from interconnected independent segments of coaxial cable with the turns ratio determined by the combination of interconnection of the conductive portion and the shield portion of the coaxial segments. The teaching in U.S. Pat. No. 4,103,267 to Olschewski attends itself to teaching a structure of a transformer for use with integrated circuit assemblies. The transformer described therein is comprised of a toroidal ferrite core affixed to a substrate having printed circuit paths affixed thereto. Primary and secondary windings are formed by interconnected segments of wire arranged to loop the core.